https://qooah.com/2011/12/04/android-2-3-%e5%ae%89%e8%a3%9d%e7%8e%87%e6%af%94%e5%8d%8a%e5%b9%b4%e5%89%8d%e5%a4%a7%e5%b9%85%e4%b8%8a%e5%8d%87/